Meeting Abstract
Cephalopods exhibit behavioral flexibility that rivals that of many mammals. The Vertical Lobe circuit (VL), a structure unique to cephalopods containing memory circuitry, parallels mammalian analogues (hippocampus) in cell number and function, but has evolved independently in the molluscan lineage. We used integrative Next-gen sequencing and bioinformatics, followed by anatomical validation using in-situ hybridization, to identify the first molecular maps of signaling molecules in cephalopod memory circuitry. We constructed, sequenced and analyzed Octopus transcriptomes of 96 tissues (VL and other neuronal tissues and periphery). We compared these transcriptomes to the Octopus genome and our gastropod neural transcriptomes including Aplysia californica. We identified 16,194 transcripts in the VL (TPM >/=1) and found 4,139 (25.5%) appear to be cephalopod-specific. Although indicators for classical neurotransmitters were present in VL circuit transcriptomes they are far less abundant than secretory peptides. We used both targeted and unbiased bioinformatics to identify 141 distinct putative secretory molecules in Octopus nervous tissues, approximately 65% of which have not been described before in any species. We have systematically cloned and mapped expression of NPs, and have localized 27 NP to the components of the VL circuit. The diversity of secretory peptides reveals multiple morphologically distinct cell types in the LE neurons, previously thought to be homogenous. This expansion of novel signaling molecules in the VL circuit is likely a key feature of the unique memory systems of cephalopods, further implying extensive parallel evolution of cephalopod brains and memory circuits in particular.
